Our asthma research program involves both exposure assessment and primary prevention components, and focuses on the relationship between exposure to common indoor allergens and asthma prevalence/morbidity. The National Allergen Survey, a descriptive study of allergen types and levels in floor and bedding dust in the nation's housing, is the first study to provide estimates of allergen exposure in the U.S. population. It encompasses 831 homes in 75 primary sampling units located throughout the country. The major endpoints are measurements of dust mite, cockroach, cat, dog, mouse, rat and fungal allergen levels, and endotoxin in dust samples collected from an array of sites in the surveyed homes. Preliminary results from analysis of dust mite allergens suggest that approximately 23% of U.S. homes have beds that contain >10mg/gram dust mite allergen (a level previously associated with symptomatic asthma) and approximately 46% of U.S. homes have beds that contain >2mg/gram dust mite allergen (a level previously associated with mite allergen sensitization). The likelihood of having a high dust mite allergen level in the bed was greater for older homes, non-western region homes, lower income households and bedrooms with higher humidity. Detectable cockroach allergen is present in approximately 6% of U.S. homes. The likelihood of having a high bed cockroach allergen levels was greater for lower income households, homes with evidence of moisture, and homes with evidence of food debris. This nationally representative survey will (a) provide current estimates of indoor allergen exposure in the U.S. population, (b) establish a database that can be used to stimulate future studies which attempt to correlate allergen exposure to disease outcome, (c) provide a baseline that can be used as a reference point for future allergen surveys, and (d) facilitate evaluation of regional, ethnic, socioeconomic, and housing characteristic differences in the allergen burden. We have also begun a clinical trial to determine if environmental intervention aimed at reducing indoor allergen levels in homes can prevent sensitization and decrease the prevalence of asthma in high risk children. Pilot studies have been conducted to test the feasibility and effectiveness of various interventions to reduce indoor allergen levels in inner-city homes. Initial efforts have focused on mitigation of cockroach and dust mite allergen. Data from these studies will improve our understanding of the complex relationships between exposure to common indoor allergens and asthma prevalence/morbidity.